Question
Will the roots of a river birch tree affect the foundation of my house if planted to closely. If so what should I do since the trees are full grown now?

Answer
No. As far as the root system the root may not give you problems with the house foundation. River birch has a width at maturity of about 20 feet and the limbs this close to the house the limbs may damage the house by rubbing on it when the wind blows. The roots will seek water and would only be a problem with a foundation if there were a leak and the roots would grow into the leak. But in generally river birch does not have a root system that damages foundations.